The present invention relates generally to a nebulizer circuit for converting water into mist for humidification purposes at a rate which is proportional to an input demand for humidification. More particularly, the invention relates to a microprocessor-controlled circuit for causing an oscillator, which normally produces a non-linear output in response to said input demand, to produce an output which is linearly proportional to said demand, to thereby provide precise control of humidification and to conserve electrical energy.
By way of background, humidification systems utilizing piezoelectric transducers to generate mist from water are driven by transistor-containing oscillators. However, the output from such oscillators is non-linear with respect to an input demand which indicates the amount of humidification required. This is due to the non-linear input-output characteristics of the transistor within the oscillator. This results in driving the transducers at much higher amplitudes than is usually required which, in turn, generates mist at much higher rates than is usually required which, in turn, results in lack of precise control of humidification and the waste of electrical energy. In the foregoing respect, for example, if the humidity sensor indicates that the actual humidity is 10% below a set humidity, the oscillator, which operates non-linearly, may drive the transducer at a rate which is equivalent to a 90%-100% requirement. This, in turn, not only requires excess electrical energy, but also causes the actual humidity to overshoot the desired level, which also results in excess electrical consumption. In contrast to the foregoing mode of operation, if the transducer could be driven at a rate which is linearly proportional to the demand for humidification, there would be no significant overshooting of the humidity or consumption of excessive amounts of electrical energy. More specifically, for example, if the sensor indicates that a 10% increase in humidity is required, if the transducer could be driven initially at an amplitude proportional to the 10% increase, and then gradually decreased in amplitude as there is a sensing of an increase in humidity, that is, linearly in relation to the input demand signal, there will be no overshooting and thus there will be precise control of the humidity and also there will be no excessive consumption of electrical energy. However, as noted above, transistor-containing oscillators are inherently not capable of producing an output which is linear in relation to a linear input.
As noted above, then, perhaps the most significant problem in a humidification system is that of achieving a linear relationship between an input demand signal (which indicates the desired mist output) and the mist output determined by the piezo-electric crystal. The problem arises because of the inherently non-linear input-output characteristics of the oscillator circuit and its main component, a transistor.
It is especially necessary to solve the "non-linearity" problem in automatic humidification systems, such as those which are used in commercial office buildings and the like, where significant amounts of electrical energy can be lost without precise control. In a typical automatic system, a humidity sensor determines the humidity level in a room, compares the measured level with a predetermined desired level, and sends a control signal to the oscillator drive circuit to adjust the amount of misting accordingly. Obviously, precise control is difficult to achieve unless there is a linear relationship between the control signal and the output of the drive circuit.
In addition to the foregoing, while residential, single-room humidifiers typically have only a single crystal and associated oscillator, commercial systems typically have many crystals which are necessary to nebulize larger volumes of liquid. A problem which arises in multiple-crystal systems is to ensure that all oscillators in the system respond to a common control signal in the same way. For example, if a common control signal is applied to eight different oscillator drive circuits, it is desired that all eight systems would produce the same amount of misting.
Finally, a problem inherent in all nebulizing systems is the generation of faults which affect system performance. These faults can take many forms. For example, the crystal or its associated drive transistor can short-circuit; the reservoir can develop a low liquid level; a power failure can occur, etc. It is desired that the system recognize certain of these faults and take appropriate corrective action.